Dallas Police Department tweeted a photo of Mark Hughes, who was at the Black Lives Matter protest, saying "This is one of our suspects. Please help us find him!"

Hughes is a black man and was wearing a camouflage t-shirt. He was also carrying a massive gun.

It was a rifle - the same kind of gun used to kill five police officers.

Hughes turned out to be innocent - something that was quickly obvious to people who spotted him in videos from the scene, in which he was clearly an onlooker and definitely wasn't shooting anyone. As soon as he realised he was a 'person of interest' he spoke to a police officer, was interrogated for half an hour, then released.

A number of Brits responded to the story asking why on earth Hughes would take a big gun to a peaceful protest. The answer, of course, is that he was in Texas where it's completely legal to openly carry a gun. You don't even need a specific permit to carry an AR-15 rifle in public - and they are reportedly a normal sight at protests in Texas.

It's hard as a Brit to imagine that. If I knew there was an active shooter on a street around me, and I saw someone with a gun, I'd be terrified. Not so in Dallas, where the 'open carry' law means that the police were hunting for men with rifles, and had their job complicated by the fact that law-abiding protestors in the crowd were doing exactly that.

Mark Hughes' brother Cory Hughes defended his brother's right to bear arms, saying: "He never thought that by exercising his right, he'd be plastered over the national media as a suspect."

But there's a sad double-standard about open carry laws that could have predicted the police's mistake in making Mark a suspect: many people speculate he was under suspicion not because of the gun, but because he was a black man carrying a gun.

The NRA has been silent over the police killing of Philando Castile, a black man shot dead by police in Louisiana, who, like Hughes, was legally carrying a gun - this time concealed. Rivero notes that Castile's weapon played a central role in his killing: Castile told the police officer he had a gun, then reached for his wallet, which is when the officer shot him four times. Yet the NRA seems unlikely to speak out over Castile's rights.

The open carry laws in some state, coupled with the alleged discrimination, show the murky reality that America has to grapple with in its gun crisis. Guns can be held by a friend or a foe, by a sniper or a peaceful protester. They can be legal or illegal, they can kill police officers and they can be used by police officers to protect or to kill civilians. A white person holding a gun has rights, a black person perhaps not so much.

One fact is less murky: Dallas's brutal shootings will spark debate over gun laws and race, but unless something radically changes, more than 30 people will continue to be shot and killed each day in the US, and America's police will continue to display brutality towards their own people on a level that's barely comprehensible to most of us in the UK. Let's hope Dallas will be the day when something changes.